In the offshore production of oil and gas, drilling and/or production equipment is typically mounted on a platform supported atop an offshore structure, often called a jacket, having a base situated on the sea floor. The oil and/or gas produced at the offshore structure commonly is transported to shore or other remote site by one or more pipelines laid on the sea floor. The pipeline(s) and the structure require different construction techniques and therefore usually are installed separately. Accordingly, it often is necessary to connect a pipeline to an offshore structure after one or both have been installed.
Various techniques heretofore have been utilized to connect underwater pipeline to an offshore structure or more specifically to production equipment located on the production platform above the surface of the water. These techniques were subject to various constraints including, inter alia, a requirement to install the structure before the pipeline is laid, a need to use divers to make a sub-sea connection, and a need to build heavy steel appurtenances into the offshore structure.
In relatively shallow water divers often are employed to connect the pipeline terminating at the base of the offshore structure to a riser flowline extending to the production equipment atop the structure. In water depths of several hundred feet or more the use of divers becomes economically unattractive. Moreover, in deeper waters, diving is dangerous and/or impractical.
Consequently, diverless or substantially diverless techniques have been developed, but again these techniques have associated therewith one or more drawbacks including in addition to those noted above: (1) installation substantially affected by surface conditions, (2) connection equipment interfering with jacket installation procedures, (3) need to remobilize a lay barge if connection made after installation of pipeline, (4) limited to relatively shallow water depths, (5) need for divers, (6) lack of flexibility in accommodating variations in positioning of jacket with respect to pipeline, (7) sensitivity to bottom currents, (8) need to handle great lengths of pipe, (9) sensitivity to poor soil and other sea floor conditions, (10) high cost in general, (11) high risk of damage to pipeline and/or structure during or after installation, (12) conflict with jacket installation operations, (13) long connection time, and (14) extensive surface support requirements.